Hybrid electric vehicles may employ belt alternator starter (BAS) technology to gain fuel efficiency of the internal combustion engine. Coming to a stop at a traffic light or during an extended idle, the engine is turned off to save fuel. As the brake pedal is released, an electric motor/generator unit restarts the engine, typically in a time of less than half of a second, making the auto start system essentially transparent to the driver. This is referred to as a stop-start strategy for enhancing fuel economy. A BAS equipped vehicle can provide 15 to 20% fuel economy gain in city driving and an overall fuel economy increase of 4 to 7%. For a baseline gasoline vehicle with fuel economy of 12.75 kilometers per liter (km/l) of gasoline (30 miles per gallon (MPG)), this is equivalent to an increase of 0.5 to 0.9 km/l (1.2 to 2.1 MPG) in fuel economy.
While the stop-start operation improves fuel economy, it may compromise passenger thermal comfort. Stopping the engine disables the belt-driven air conditioning (A/C) compressor, resulting in interruption of cooling for the passenger compartment. Typically, vehicle manufactures rely on the thermal inertia of the air conditioning evaporator to provide some residual cooling during the period when the engine is stopped. The evaporator residual cooling time is typically limited to 25 seconds or less before the discharge temperature of the evaporator rises above a level that no longer provides the desired cooling. When the evaporator is warmed up to a specified air discharge temperature, the engine is restarted to drive the A/C compressor to provide cooling. This periodic restarting of the engine under idle conditions undermines fuel economy improvement that can be achieved by the hybrid electric vehicles.
The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions.